1. Field of the Invention
The invention relates to an electromagnetic valve drive apparatus of an internal combustion engine and, more particularly, to an internal combustion engine electromagnetic valve drive apparatus in which intake valves and/or exhaust valves provide for a plurality of cylinders with valve-opening electromagnetic valves, valve-closing electromagnetic valves, and closed valve state holding mechanisms that do not employ electromagnetic force, and in which drive circuits are provided for the electromagnetic valves, whereby the valves are opened and closed.
2. Description of the Related Art
The disclosure of Japanese Patent Application No. HEI 11-347396 filed on Dec. 7, 1999 is herein incorporated by reference.
Known electric valves are used as intake valves or exhaust valves of internal combustion engines. An example of electromagnetic valves an armature displaceable with a valve body, a pair of electromagnetic coils disposed above and below the armature, and springs that urge the valve body toward a neutral position, as described in Japanese Patent Application Laid-Open No. HEI 8-284626.
In the electromagnetic valve, the valve body and the armature are held at the neutral position by the forces from the springs when neither one of the electromagnetic coils is supplied with an exciting current. When the upper electromagnetic coil is supplied with an exciting current, the valve body and the armature are magnetically drawn toward the upper electromagnetic coil. Conversely, when the lower electromagnetic coil is supplied with an exciting current, the valve body and the armature are magnetically drawn toward the lower electromagnetic coil. Therefore, this conventional electromagnetic valve is able to open and close the valve body by supplying suitable exciting current alternately through the electromagnetic coils.
In view of the responsiveness of the electromagnetic valve in opening and closing actions, durability of the electromagnetic valve, and the like, it is necessary to control the quantity of current through the electromagnetic coils with a high responsiveness. Thus, the exciting current supplied to each electromagnetic coil is controlled by an H-shape bridge circuit. The H-shape bridge circuit is formed by the terminals of the electromagnetic coils and four switching elements, each of which is provided between one of the terminals of the electromagnetic coil, and a high potential side or a low potential side.
In the H-bridge circuit, a voltage can be applied to the electromagnetic coil to supply an exciting current in a forward direction by turning on a pair of switching elements located diagonally about the electromagnetic coil and turning off the other pair of switching elements. By reversing the on/off states of the two pairs of switching elements, a voltage in a direction opposite to the exciting current can be applied to the electromagnetic coil. Therefore, by switching the on/off states of the switching elements of the H-bridge circuit, it is possible to quickly discontinue the production of electromagnetic force from the electromagnetic coil, and to supply a reverse current through the electromagnetic coil immediately after the discontinuation of electromagnetic force. Conversely, when a current is flowing through the electromagnetic coil in the direction opposite to the exciting current, it is possible to quickly discontinue the production of electromagnetic force from the electromagnetic coil in the reverse direction, or to deliver a current through the electromagnetic coil in the forward direction immediately after the discontinuation of reverse electromagnetic force, by applying a voltage to the electromagnetic coil in the forward direction.
In this manner, the quantity of current through each electromagnetic coil can be controlled with a increased responsiveness.
However, in order to achieve such a increased responsiveness, it is necessary to provide four switching elements for each electromagnetic coil as described above. Because each electromagnetic valve needs to have two electromagnetic coils, such as, a valve-closing electromagnetic valve and an valve-opening electromagnetic valve, the total number of switching elements needed for each electromagnetic coil becomes eight. Therefore, in the case of a four-cylinder four-valve engine, 128 switching elements are needed for the 16 valves, thus leading to a size increase and a cost increase of the electromagnetic valve drive apparatus.
In order to solve this problem, a drive apparatus for electromagnetic valves are known in which the number of switching elements is reduced while the functions of the electromagnetic valve drive apparatus are maintained, as described in Japanese Patent Application Laid-Open No. HEI 11-166657. This drive apparatus for electromagnetic valves has a drive circuit. The drive circuit includes series circuits having three switching elements connected in series and arranged in parallel for a group of electromagnetic valves that perform identical operations. In this circuit construction, switching elements are used collectively for a plurality of electromagnetic valves. That is, this construction reduces the need to provide dedicated switching elements for each electromagnetic valve. Therefore, if this three-switching-elements-in-series type drive circuit is applied to a four-cylinder four-valve engine, only 72 switching elements are needed for the 16 valves. The size and cost of the electromagnetic valve drive apparatus may be reduced.
However, even with the sharing of switching elements, the total number of switching elements employed is still large. A need has arisen for a further reduction in the number of switching elements to reduce the size and cost of the electromagnetic valve drive apparatus.
Accordingly, it is an object of the invention to provide an electromagnetic valve drive apparatus of an internal combustion engine that allows a further reduction in the number of switching elements.
To achieve the aforementioned and other objects, an electromagnetic valve drive apparatus of an internal combustion engine includes valve-closing electromagnetic coils provided for intake valves and/or exhaust valves. The valves are provided for a plurality of cylinders. The electromagnetic drive apparatus includes valve-opening electromagnetic coils provided for the intake valves and/or the exhaust valves, and a mechanism that holds the intake valves and the exhaust valves in a closed state without using an electromagnetic force. The electromagnetic valve drive apparatus also includes a drive circuit provided for the electromagnetic coils, so that the electromagnetic valve drive apparatus opens and closes the valves. The drive circuit is provided for a valve group of valves, including a plurality of valves that perform identical operations and has at least one valve whose open period does not overlap an open period of the plurality of valves that perform identical operations. In the drive circuit, a plurality of series circuits are connected in parallel between a high electric potential side and a low electric potential side. Each series circuit is formed by connecting a plurality of switching elements in series. The electromagnetic coils are provided individually for the valves of the valve group and are connected between the series circuits.
Thus, the drive circuit is provided collectively for a valve group that consists of a plurality of valves that perform identical operations and at least one other valve whose open period does not overlap the open period of the valves that perform identical operations. The drive circuit is constructed to have a plurality of series circuits connected in parallel between the high electric potential side and the low electric potential side. Each series circuit is formed by connecting a plurality of switching elements in series. The electromagnetic coils are provided individually for the valves of the valve group and are connected between the series circuits.
The electromagnetic coils driven by the above-described drive circuit include the electromagnetic coils used for the valves that perform identical operations, and the electromagnetic coils of at least one valve whose open period does not overlap the open period of the valves that perform identical operations. Due to the relationship between the two sets of valves in which their open valve periods do not overlap each other, the acting periods of the switching elements for controlling current through the electromagnetic coils can be completely separated for the two sets of valves so as to open the valves and hold the valves in the open state. Therefore, in the drive circuit, switching elements can be shared by the two sets of valves, whose open periods do not overlap each other.
Furthermore, in view of two valves whose open periods do not overlap each other, another valve that performs an operation identical to that of a first valve of the two valves requires the same operation of the switching elements as that required by the first valve. Because of this valve relationship, the sharing of a switching element in the drive circuit also is possible between valves that perform identical operations.
With respect to the second valve of the two valves whose open periods do not overlap each other, the valve that performs an operation identical to that of the first valve has a relationship in which the open period of the valve does not overlap the open period of the second valve, so that the sharing of a switching element in the drive circuit also is possible between the valve and the second valve.
Thus, a valve whose operation is identical to the operation of one of two valves allows the sharing of a switching element for a valve-opening operation with respect to either one of the two valves.
Therefore, since the sharing of switching elements can be achieved by providing the drive circuit collectively for a group of valves consisting of a plurality of valves that perform identical operations and at least one other valve whose open period does not overlap the open period of the valves that perform identical operations, the number of switching elements employed to open the valves may be reduced.
The closed periods of the valves of the valve group overlap each other. However, due to the provision of the mechanism for holding the valves in the closed state without using electromagnetic force, it may necessary to drive a switching element during the closed valve period. Therefore, the activation of the electromagnetic coils is needed only during the closing action of the valves. Because the closing action occurs at the end of each open valve period, the closing action period of valves does not overlap the closing action period of other valves whose open period does not overlap the open period of the aforementioned valves. Therefore, the sharing of switching elements for closing the valves can be achieved as described above in conjunction with the valve opening operation.
Therefore, the sharing of switching elements can be achieved by providing the drive circuit collectively for a group of valves consisting of a plurality of valves that perform identical operations and at least one other valve whose open period does not overlap the open period of the valves that perform identical operations. The number of switching elements employed to open and close the valves may be reduced.
Thus, the drive circuit is able to supply current and discontinue current through the electromagnetic coils of valves at appropriate timings, through the switching operations of the reduced number of switching elements that are shared by the electromagnetic coils.
Hence, the invention reduces the number of switching elements employed, and therefore allows a size reduction and a cost reduction of the electromagnetic valve drive apparatus.
Furthermore in the electromagnetic valve drive apparatus of an internal combustion engine, the drive circuit may be collectively formed by at least one series circuit connection that is made only via the electromagnetic coils provided for the plurality of valves that perform identical operations, and at least one other series circuit connection that is made only via the electromagnetic coils provided for at least one valve whose open period does not overlap the open period of the plurality of valves that perform identical operations.
The connections between the series circuits constituting the drive circuit may be formed by two kinds of circuit connections. The circuit connections are made via the electromagnetic coils provided for a plurality of valves that perform identical operations, and inter-series circuit connections made only via the electromagnetic coils provided for at least one valve whose open period does not overlap the open period of the plurality of valves. As the drive circuit formed by the two kinds of circuit connections is provided collectively for the group of valves, switching elements can be shared by valves of the valve group in controlling the quantity of current through the electromagnetic coils. Therefore, the number of switching elements employed may be reduced, thereby allowing a size reduction and a cost reduction of the electromagnetic valve drive apparatus.
The electromagnetic valve drive apparatus of an internal combustion engine may be include the drive circuit collectively formed by alternately disposing circuit connections. The circuit connections are made via the electromagnetic coils provided for a plurality of valves that perform identical operations and via the electromagnetic coils provided for at least one valve whose open period does not overlap the open period of the plurality of valves.
The two circuit connections may be arranged so that the two kinds alternate. With this arrangement, the drive circuit allows the sharing of switching elements among valves of the group in the control of the quantity of current through the electromagnetic coils. Therefore, the number of switching elements employed can be reduced, so that the electromagnetic valve drive apparatus can be reduced in size and cost.
Furthermore, in the electromagnetic valve drive apparatus of an internal combustion engine, the drive circuit may also be collectively formed in such a fashion that the circuit connections are disposed separately with a single series circuit defining a boundary there between.
The circuit connections of the two kinds may be arranged in such a fashion that the two kinds are separated by a single series circuit defining a boundary. That is, one group of circuit connections may be disposed as a unit at one side of a series circuit, and the other group of circuit connections may be disposed as a unit at the other side of the series circuit.
With this construction, the drive circuit provided collectively for a group of valves allows the sharing of switching elements among valves of the group in controlling the quantity of current through the electromagnetic coils. Therefore, the number of switching elements employed can be reduced, so that the size and cost of the electromagnetic valve drive apparatus also can be reduced.
Furthermore, in the electromagnetic valve drive apparatus of an internal combustion engine, each series circuit may be connected to another series circuit via electromagnetic coils provided for a single valve.
Thus, it is possible to connect each series circuit to another series circuit via the electromagnetic coils of a single valve instead of electromagnetic coils of difference valves. This construction facilitates the sharing of switching elements, and, therefore, may reduce the number of switching elements.
For example, if each series circuit is connected to another series circuit via two electromagnetic coils of a single valve, such as, a valve-opening electromagnetic coil and a valve-closing electromagnetic coil of the valve, the sharing of a series circuit becomes possible between the valve-opening electromagnetic coil and the valve-closing electromagnetic coil. Thus, such a connection construction may reduce the number of switching elements employed.
Furthermore, in the electromagnetic valve drive apparatus of an internal combustion engine, each series circuit may be formed by connecting three switching elements in series, and end portions of the electromagnetic coils may be connected to series connecting portions between the switching elements so as to form circuit connections.
The circuit connections may be formed by connecting the end portions of the electromagnetic coils to the series connecting portions between the switching elements of the series circuits formed by connecting three switching elements.
With this construction, the drive circuit provided collectively for a group of valves allows the sharing of switching elements among valves of the group in controlling the quantity of current through the electromagnetic coils. Therefore, the number of switching elements employed can be reduced, so that the size and cost of the electromagnetic valve drive apparatus can be reduced.
The above-described construction makes it possible to realize a mode of supplying reverse current through the electromagnetic coils in the switching control of the switching elements.
Furthermore, the at least one series circuit may also be formed by connecting three switching elements in series, and at least one other series circuit is formed by connecting two switching elements and a diode in series. The diode is disposed between the two switching elements in such a direction as to allow a current to flow from the low electric potential side to the high electric potential side. Circuit connections are formed by connecting end portions of the electromagnetic coils to series connecting portions between the switching elements of the at least one series circuit or to series connecting portions between the diode and the switching elements of the at least one other series circuit.
With the two kinds of series circuits, the circuit connections may be formed by connecting the end portions of the electromagnetic coils to the series connecting portions between the switching elements or to the series connecting portions between the diode and the switching elements.
Thus, using low-cost diodes in place of switching elements, the electromagnetic valve drive apparatus is able to control the quantity of current through the electromagnetic coils. Therefore, the number of switching elements employed is reduced so that the size and cost of the electromagnetic valve drive apparatus can be reduced.
Still further, the drive circuit may be provided collectively for a valve group of four valves consisting of two valves that perform identical operations on a cylinder and two valves of another cylinder whose open valve period does not overlap the open valve period of the two valves. In the drive circuit, five series circuits are formed by connecting three switching elements in series, and are connected in parallel between the high electric potential side and the low electric potential side, and electromagnetic coils provided for the four valves are connected between the five series circuits.
More specifically, the drive circuit may be provided collectively for a valve group of four valves consisting of two valves that perform identical operations on a single cylinder and two valves whose open period does not overlap the open period of the two valves. In the drive circuit, five series circuits are formed by connecting three switching elements in series, and are connected in parallel between the high electric potential side and the low electric potential side. The electromagnetic coils provided individually for the four valves are connected between the five series circuits. In this manner, switching elements can be shared by valves of the group.
With the above-described construction, the electromagnetic valve drive apparatus is able to control the quantity of current through the electromagnetic coils. Therefore, the number of switching elements employed can be reduced, so that the size and cost of the electromagnetic valve drive apparatus can be reduced.
Furthermore, the valve-opening electromagnetic coil and the valve-closing electromagnetic coil of each valve may be connected between different pairs of series circuits.
If the two electromagnetic coils of a single valve are connected between different pairs of series circuits as mentioned above, the number of switching elements and electromagnetic coils provided along each current path for activation of the electromagnetic coils can be reduced. Therefore, it becomes possible to reduce the loss of supplied current.
Still further, in the electromagnetic valve drive apparatus of an internal combustion engine, each series circuit may be formed by connecting two switching elements, and circuit connections may be formed by connecting the end portions of the electromagnetic coils to the series connecting portions between the switching elements.
By connecting the end portions of the electromagnetic coils to the series connecting portions between the two switching elements of the series circuits each formed by connecting two switching elements as described above, it becomes possible to realize a mode of supplying reverse current through the electromagnetic coils particularly in the switching control of the switching elements.
Furthermore, the electromagnetic valve drive apparatus of an internal combustion engine also may have the following construction. That is, at least one series circuit is formed by connecting two switching elements, and at least one other series circuit is formed by connecting in series one switching element and a diode. The diode is disposed in such a direction as to allow a current to flow from the low electric potential side to the high electric potential side. The series circuits are connected by connecting end portions of electromagnetic coils to a series connecting portion between the switching elements of the series circuit or to a series connecting portion between the switching element and the diode of the other series circuit.
With the two kinds of series circuits as described above, the circuit connections may be formed by connecting the end portions of the electromagnetic coils to the series connecting portion between switching elements of at least one series circuit or to the series connecting portions between the switching element and the diode of at least one other series circuit.
Thus, using low-cost diodes in place of switching elements, the electromagnetic valve drive apparatus is able to control the quantity of current through the electromagnetic coils. Therefore, the number of switching elements employed is further reduced, so that the size and cost of the electromagnetic valve drive apparatus can be further reduced.
Still further, the electromagnetic valve drive apparatus of an internal combustion engine may have the following construction. That is, the drive circuit is provided collectively for a valve group of four valves consisting of two valves that perform identical operations on a cylinder and two valves of another cylinder whose open valve period does not overlap the open valve period of the two valves. In the drive circuit, nine series circuits are formed by connecting two switching elements in series and are connected in parallel between the high electric potential side and the low electric potential side. The nine series circuits are connected via electromagnetic coils provided for the four valves.
More specifically, the drive circuit may be provided collectively for a valve group of four valves consisting of two valves that perform identical operations on a single cylinder and two valves whose open period does not overlap the open period of the two valves. In the drive circuit, nine series circuits are formed by connecting two switching elements in series and are connected in parallel between the high electric potential side and the low electric potential side. The electromagnetic coils provided individually for the four valves are connected between the nine series circuits. In this manner, switching elements can be shared by valves of the group.
With the above-described construction, the electromagnetic valve drive apparatus is able to control the quantity of current through the electromagnetic coils. Therefore, the number of switching elements employed can be reduced, so that the size and cost of the electromagnetic valve drive apparatus can be reduced.
Furthermore, in the electromagnetic valve drive apparatus of an internal combustion engine, the switching elements may have built-in diodes, and may be disposed in such a direction that a current is allowed to flow from the low electric potential side to the high electric potential side by the diodes.
Therefore, it becomes possible to perform a more complicated control of current through the electromagnetic coils.
The electromagnetic valve drive apparatus of an internal combustion engine may further include a mechanism that holds the electromagnetic coils in an open state without using an electromagnetic force.
Thus, in addition to the mechanism for holding the valves in the closed state without using electromagnetic force, the mechanism for holding the valves in the open state without using electromagnetic force may be provided.